Conventional laundry dryers have a drying chamber in which a perforated drum is rotated to tumble the laundered goods. A combustion unit is provided for heating the ambient makeup air to a temperature suitable for drying the laundered goods. The combustion unit conventionally includes a pair of gas burners which are arranged in side-by-side relation in the airflow path between an ambient makeup air inlet and the drying chamber. A blower or the like is provided for circulating the heated air from the combustion unit through the drying chamber and exhausting the moisture-laden airflow to the environment.
It is known that the fuel efficiency of a laundry dryer may be improved by reclaiming heat from the moisture-laden exhaust airflow. For example, Cloud et al U.S. Pat. No. 3,959,892 introduces a portion of the exhaust airflow into the combustion chamber at a point downstream from the first and second burners and upstream of the inlet to the drying chamber.
Another prior art heat reclaimer for a laundry dryer is shown in Thompson U.S. Pat. No. 3,969,070. Thompson defines a recycle manifold by mounting a housing in spaced relation above the top wall of the combustion chamber to define an airflow passage in heat exchange relation with the top wall of the combustion chamber. A portion of the exhaust airflow is circulated through the recycle manifold and is then mixed with the heated makeup air immediately adjacent the inlet to the drying chamber.
One disadvantage of the prior art recirculating devices is that the recirculation of 45 to 75% of the moisture-laden exhaust airflow into the drying chamber substantially reduces the volume of makeup airflow to the two gas burners. Accordingly, the gas burners may be starved for makeup air with the result that the airflow in the combustion chamber my stagnate and a portion of the heat generated therein is lost by conduction through the walls of the dryer or through reverse airflow through the makeup air inlet. Furthermore, a so-called lazy flame condition may result in which the airflow across the burners is not sufficient to forcibly draw the combustion products toward the drying chamber inlet.
Furthermore, the aforedescribed prior art heat reclamation devices do not provide for entrapment of lint which may be present in the exhaust airflow, particularly where the lint filter of the dryer is not properly maintained.